Christoph Zauner CRYOGENIC MATERIAL TESTING SPECIAL REQUIREMENTS FOR TEST SETUP AND TEST PERFORMANCE DEMONSTRATED ON ADDITIVE MANUFACTURED LIGHTWEIGHT ALLOYS
Index Demand of cryogenic testing Cryogenic temperature ranges and cooling methods Building cryogenic test setups Material Design Performing cryogenic tests Example(s)
Demand on cryogenic testing Space: liquid propellant tank structures (20K for LH) cryogenic instruments Fusion Research: superconducting magnet structures (4K) Automotive liquid hydrogen tank structures Goal: material characterisation component / structure verification
Temperatures and cooling methods Overview on typical temperature ranges, cooling methods and cooling equipment Temperature Method Equipment hot to -140 C (-180 C) evaporative cooling of liquid nitrogen thermal chamber -196 C (77K) direct immersion in liquid nitrogen test dewar -196 C to -263 C (10K) evaporative cooling of liquid helium helium dewar gas phase -269 C (4K) direct immersion in liquid helium helium dewar liquid phase
Cooling Fluids Comparison of Nitrogen and Helium Temperature Nitrogen Helium Ratio He / N2 Temperature -196 C / 77K -263 C / 4K - Density liquid in kg/l 0,8076 0,1785 0,22 Heat of vaporisation in kj/kg 199 21,1 0,11 Cost per liter in 0,1 3 30 Cost per cooling 1kg stainless steel to liquid temperature in Delivery Gas recoverage 0,06 108 1677 by truck stored in big tanks not required On-site helium liquefier strongly recommended
Thermal chamber (RT to -140 C) + - Wide temperature range, and integrated easy control Feedthrough of fixed and moving test machine interface Limited cryogenic range (commercial -140 C, self build to -180 C)
Direct immersion in liquid nitrogen + - High cooling rate Flexible cryostat design Fixed temperature Risk of thermoelastic damage of the test setup / test machine during cooling down
Evaporation of liquid helium + Wide temperature range (77K to ~10K) - Temperature gradient along specimen needs to be compensated by electrical heating Low cooling rate High Cost Temperature Control and LHe flow control required
Direct immersion in liquid helium + - Lowest cryo-temperature Fixed temperature Risk of thermoelastic damage during cooling down High cost Baffle system required
Cryogenic test setups - Materials Stainless steel is mainly used Low embrittlement and thus robust against transient forces during specimen failure Low thermal conductivity (good isolation of load bearing parts)
Cryogenic test setups - Design guidelines Mechanical design mass is money at LHe! FEM to identify load paths and optimize w.r.t. mass (morphological optimization) Assess maximum load capacity of test setup at different temperatures (w.r.t. temperature depended yield strength) Take care not to overload stainless steel setups at RT or high temperature
Cryogenic test setups - Design guidelines Thermal design FEM to identify temperature distribution and achievement Evaluate cooling time and cost per test
Cryogenic setups Vacuum environment Low convective heat transfer Two axis friction test 2MN/2MN at -190 C under vacuum vacuum sealing in cryogenic temperature: CF flanges Internal and external cooling of load bearing paths Heat transfer coefficient from 150 C to 250 C at 50kN LN2 tank mobile 100l LN2 tank fixed 4200l LN2 indirect cooling vacuum chamber LN2 N2 direct cooling channels NSE Interface LN2-outlet
Cryogenic test performance Select temperature compatible strain gauges, extensometers and temperature sensors Protect test machine from condensed water Monitor oxygen in test lab Take into account liquid oxygen and liquid hydrogen Provide gaps for different thermal expansions Don t block test machine during cooling down and heating up high risk of overload and destruction Stiffness Temperature CTE Vetronit Isolation Protective Foil
Application example 3D printed metals Test setup design Tension Compression Shear Pin Bearing
Application example 3D printed metals Temperature levels RT 200K (-73 C) 77K (-196 C) 4K (-269 C)
Strain rate [s-1] Force [N] Stress [MPa] Temperature [ C] Stress [MPa] Application example 3D printed metals Test performance Cooling down Strain control during yield Switch to stroke control after Rp0.2 has been reached Retract extensometer Load until failure 600 500 400 300 200 100 Stress vs Strain - Extensometer 0 0 0.005 0.01 0.015 Strain [mm/mm] 4 x 10-4 3 2 Strain rate history -60-65 -70-75 T specimen top T specimen bottom Limits -80 0 200 400 600 Time [s] 8000 7000 6000 5000 4000 3000 600 500 400 300 200 100 Stress vs Crossheadtravel 0 0 1 2 3 4 Stroke [mm] E t = 78305 MPa TYS t = 557 MPa TUS t = 591 MPa R square=0.9999 TYS u = 538 MPa TUS u = 571 MPa e=10.5% 1 2000 1000 0 0 10 20 30 40 Time [s] 0 0 200 400 600 Time [s]
Keep in mind: Safety first Thank you for your attention! Questions?
Further Cryogenic Test Examples
Further Cryogenic Test Examples 2MN 900kN Leakage test of LN2 cryostat Two axis cryogenic loading test